Top nozzle of multistage diffusion pump



Dec. 24, 1968 HlRoKl oKAMo-ro ETAL 3,417,914

TOP NOZZLE' OF MULTISTAGE DIFFUSION PUMP Filed June 6, 1967 rbmL/d-m;

United States Patent Office 3,417,914 Patented Dec. 24, 1968 ABSTRACT F THE DISCLOSURE A multistage diffusion pump having a novel top nozzle which automatically opens the jet clearance thereof at its normal operation time, and also automatically closes the clearance at its stopping time, by means of a movable nozzle cap driven by a thermal moving device utilizing a ring of ferromagnetic substance, a bimetallic plate or a like spiral band.

Background of the invention This invention relates to a diffusion pump and more particularly to an improved top nozzle of a multistage diffusion pump.

A diffusion pump is widely used in the vacuum deposition process and elect-ron tube exhaust which irequire a very low pressure. The -principle of the diffusion pump generally consists in boiling and evaporating a lpumping uid such, for example, as a thoroughly purified low vapor pressure organic fluid or mercury in the boiler of said pump, vigorously ejecting said vapor through a narrow opening towards the high pressure side to compress gas molecules diffusing from the vacuum vessel, draining out said gas molecules by means of an auxiliary pump connected with said diffusion pump, subsequently cooling and liquefying said vapor by a condenser installed nearby, and returning the vapor thus liquefied to the boiler, thus continuously carrying out evacuation by the repeated cycle of evaporation and condensation of the pumping fluid. To obtain especially high vacuum, however, a diffusion pump provided with jet nozzles arranged in two or three stages is often employed.

In this case, it is required to minimize the back streaming of the pumping fluid to the high vacuum side as far as possible in order to avoid the contamination of the articles loaded in the vacuum vessel. This is because, if any amount of pumping fluid flows back into the vacuum vessel, it will adsorb to the surface of the loaded articles, such as .a substratum to be vacuum-deposited or the electrodes of an electron tube, and spoil the properties of these articles.

The aforesaid back streaming during the operation of a multistage diffusion pump is deemed mainly due to the second evaporation of the dewdrops of the pumping fluid which has been condensed and deposited in an outwardly pushed manner on the lip of top jet nozzle which closes to the vacuum vessel, or also due to irregularities in the velocity and direction of the -vapor streams ejected from the top nozzle which ow along the walls of said top nozzle. Many of these phenomena appear most prominently when the diffusion pump is not operated under the normal conditions, that is to say, when said operation has just started or stopped. Of course, such phenomena also take place at the lower nozzles, but they are not so noticeable as at the top nozzle.

As a means to prevent the back streaming of the pumping uid, some of the common multistage diffusion 'pumps comprise improvements such, for example, as an attachment of a small heater to the nozzle section to prevent the condensation and deposition of oil or mercury on the top nozzle lip, or an improvement of the nozzle construction by tting a water-cooled cap to the top nozzle, condensing and fixing at this point the vapor molecules of the uid thereby preventing them from being conducted to the vaccum vessel.

Even though these devices are effective to some extent in reducing the back streaming from the top nozzle at the end of the pumping operation, they are not satisfactory, because the amount of back streaming is still large at the beginning of the pumping operation.

Summary of the invention According to the present invention there is provided a multistage diffusion pump having a novel top nozzle which opens automatically the jet clearance thereof at its normal operation time, and closes the clearance automatically at its stopping time, by means of a movable nozzle cap driven by a thermal moving device. As the thermal moving device, a couple of rings can be used, one being a permanent magnet and the other being a ferromagnetic substance having a Curie point of to 250 C., and connected with each other by a spiral spring, a bimetallic plate or a like spiral band. By means of these novel top nozzles, the back streaming of -pumping fluid into the vacuum vessel can be substantially prevented.

The principal object of the invention is to provide a multistage diffusion -pump having a novel top nozzle capable of automatically opening and closing by a movable nozzle cap.

Brief description of the drawing FIG. 1 shows a schematic elevational sectional view of the diffusion -pump of the prior art,

FIG. 2 shows an elevational sectional view of one embodiment of the top nozzle according to the present invention,

FIG. 3 is an elevational sectional view of another embodiment of the top nozzle according to the present invention,

FIG. 4 is an elevational sectional view of still another embodiment of the top nozzle according to the present invention, and

FIG. 5 is an indicative diagram showing changes with time in the back streaming yrate of the pumping fluid into the vacuum vessel when the diffusion pump of FIG. l and a diffusion pump having a top nozzle prepared by the present invention are employed respectively.

Descrz'plion of the preferred embodiment The present invention is an improvement on a multistage diffusion pump using an organic liquid of low vapor pressure or mercury as a pumping fluid, of which nozzle placed close to the vacuum vessel connected to said pump, namely, the top nozzle, is not fixed firmly, but is made to move thermally by the vapor of the pumping uid and automatically open or close when the temperature reaches a certain level. Consequently when the temperature of the top nozzle is below a certain level, that is when the diffusion pump has just started o1 stopped, the vapor of the pumping fluid does not come out of said nozzle owing to its automatic closing, bul flows through the lower nozzle. 'Consequently it is possi ble substantially to reduce the back streaming of the pumping fluid into the vacuum vessel caused by tht condensation of its vapor on the outside of the top nozzll or by confused vapor streams which result from th irregular amounts of the pumping fluid evaporated.

The mechanims of the multistage diffusion -pump of the prior art will be first explained briefly hereinafter, before proceeding to the detailed explanation of the construction ofthe top nozzle according to the present invention. As shown in FIG. 1, cap 2 defining jet clearance 1 is fixed by means of supporting rod 5 to supporting member 4 fitted to chimney 3 in a manner to hang over the upper end of chimney 3, leaving a narrow space. Most of the vapor of pumping fluid 8 heated by heater 6 ascends from boiler 7 and spouts out of the jet clearance of the top nozzle and the remainder thereof from lower nozzle 9. These ejected vapors then compress the gas discharged yfrom vacuum vessel 10 and expel it towards gas exit 11 connected with an auxiliary pump (not shown). In the meantime the vapor of the pumping fluid is condensed by condenser 12 and returns to the boiler 7 circulatingly.

FIG. illustrates changes with time in the quantities of the pumping ud vapor fiowing back to the vacuum vessel in the operation of the diffusion pump of the prior art and that of the present invention, the inlet diameter of both pu-mps being 100 mm., and silicone oil being employed as a pumping fluid. A is the back flowing `curve in the case of prior arts using a diffusion pump shown in FIG. 1, and curve C represents the corresponding temperature of the top nozzle.

As clear from curve A, the back streaming of the pumping fluid vapor displays a conspicuous increase during the period of from switch-on of the heater till the arrival of the top nozzle temperature at the normal condition, and also during the period the temperature of the top nozzle subsides subsequent to switch-off of the heater.

According to the present invention, however, the cap 2 defining the jet clearance 1 is not fixed firmly to the chi-mney 3, but the jet clearance is made to open or close automatically depending on the temperature of the top nozzle by means of a suitable thermal moving device. Thus when the temperature of the top nozzle is raised to the temperature corresponding to the moment X after the heater is switched on as is shown in FIG. 5, the jet clearance opens by means of said thermal moving device to start the normal operation. On the other hand, when the heater is switched off at the moment of Y point, the jet clearance closes automatically at Z point, and the volume of the pumping fluid vapor progressively decreases and flows out only through the lower nozzle 9. Accordingly the volume of the pumping fluid vapor owing back to the vacuum vessel presents its change with time just like to the curve B in FIG. 5, reducing the peak volumes of the back streaming immediately after the switch-on and olf.

Further description will hereinafter be given of a -few embodiments of the present invention with reference to the drawing. Referring first to FIG. 2 showing one embodiment of the top nozzle, a permanent magnet ring 26 is fixed to the inside of cap 22, and on the other hand an annular element 27 of the ferromagnetic substance having a Curie point of from 150 to 250 C. is fitted to the upper end of chimney 23 in such a way that it attracts said permanent magnet ring 26. A supporting rod 25 provided with a spiral spring 28 is fixed at its upper end to said cap 22, and the lower end of iaid supporting rod 25 is inserted into the supporting nember 24 fixed to the chimney 23.

By the magnetic attraction between the permanent nagnetic ring 26 and the ferromagnetic substance 27, he top nozzle 21 remains closed till the temperature of he substance 27 attains its Curie point by the vapor of he pumping fiuid, preventing the passage of the pumpng uid vapor therethrough. When the evaporation of he pumping fiuid becomes more active and ferromag- Letic substance 27 is heated to the temperature of its urie point, said substance 27 is rapidly reduced in iagnetism, and consequently the cap 22 is pushed us by the restoration -force of spring 28, opening the nozzle 21 as shown in FIG. 2 to eject vigorously the vapor of the pumping fluid downwards through the nozzle 21 bringing the diffusion pump to the normal operating state.

When the operation of the diffusion pump is stopped by switching off the heater and the temperature of ferromagnetic substance 27 drops to a value below its Curie point, its magnetism is recovered so that the attraction between the substance 27 and permanent magnet ring 26 is again effected. The top nozzle closes the vapor stream ejected therefrom is stopped and gradually de` creases while it goes out from the lower nozzle. Thus the considerable back streaming of the pumping fluid vapor to the vacuum vessel is abstructed which has been observed with the diffusion pump of the prior art at its start and stop.

Referring to FIG. 3 showing a second embodiment of the top nozzle of the present invention, the cap 32 s suspended on a bimetallic plate 36 by means of two supporting members 37 and 38, each respectively fixed on the both ends of the bimetallic plate 36 mounted on the upper end of short supporting rod 35 which is fixed to the supporting member 34 fitted into the chimney 33, and the jet clearance 31 is closed. At temperatures below a certain level of the bimetallic plate 36 maintains its downward curve, but when the temperature of the plate 36 is raised following the start of pumping operation, the plate 36 begins to curve upward so as to lift the cap 32, opening the jet clearance 31 to start the normal operation. On the other hand, when the pumping operation is stopped, the bimetallic plate 36 returns to the original position, closing the jet clearance 31 to prevent the vapor of the pumping fluid from owing out therefrom.

Finally, a third embodiment of the top nozzle ofthe present invention will be explained with reference to FIG. 4. The cap 42 is fixed in an airtight manner to the enlarged lip of chimney 43, and the periphery 41 of the lip of chimney corresponding to the jet clearances 1, 21 and 31 shown in FIGS. l to 3 respectively, is closed at all times. Instead of those clearances a plural number of jet holes 48 are bored in the enlarged walls of the chimney. A spiral bimetallic band 46 is fixed to the short supporting rod 45 on the supporting member 44 fitted to the chimney 43. A revolvable plug 47 is fixed to the upper end of the spiral bimetallic band 46, and provided with the same number of jet holes 49 as those on the enlarged chimney wall in such a way that when the wall of revolvable plug 47 slides along the inner wall of the enlarged chimney, each of said jet holes 48 accords with the corresponding jet hole 49 on the enlarged chimney wall.

When the diffusion pump is not in operation, each jet hole 48 is kept away from other jet holes 49, so that the vapor of the pumping fiuid cannot pass through these holes. However, when the temperature of spiral bimetallic band 46 rises higher as the pumping operation proceeds, the revolvable plug 47 begins to revolve a little, and each jet hole 48 begins to accord with the corresponding jet hole 49, and consequently the vapor of the pumping fluid s ejected out from the holes of the enlarged chimney wall to start the normal operation of the pump. When the pumping operation is stopped the spiral bimetallic band 46 returns to the original state, completely preventing the vapor of the pumping id from owing out of jet holes 48.

It will be understood that various changes and modifications may be made without departing from the scope of the invention as defined in the appended claims. It is intended therefore that all the matters contained in the foregoing description and in the drawings are to be interpreted as illustrative only and not as limitative of the invention.

What is claimed is:

1. A multistage vacuum diffusion pump having a top nozzle member with a fixed portion and a movable portion, movement of said movable portion relative to said xed portion causing the jet clearance to vary, a temperature responsive actuator for moving said movable portion relative to said xed portion; whereby said jet clearance opens automatically during normal pump operation and temperature and closes automatically when the pump is shut down.

2. A pump as claimed in claim 1, comprising a ring of permanent magnetic material fixed to an inner side of said movable portion, a chimney having a ring of ferromagnetic material at the top of said chimney and a spiral spring connecting said permanent magnetic ring and said ferromagnetic ring.

3. A pump as claimed in claim 1, comprising a bimetallic plate upon which said movable portion is supported and a chimney supporting said bimetallic plate.

4. A pump as claimed in claim 1, comprising a chimney with an enlarged top wall, a cap fixed to said chimney,

said chimney having a plurality of jet holes therethrough, said movable portion comprising a revolvable plug having a plurality of outow holes in a side wall thereof corresponding to said jet holes, and a spiral bimetallic element connecting said revolvable plug to a supporting member liXed to said chimney.

References Cited UNITED STATES PATENTS 2,150,685 3/1939 Hickman 230--101 2,806,644 9/1957 Warren 230-101 2,894,680 7/1959 Hiesinger 230-101 2,903,181 9/1959 Giepen 230--101 3,344,979 10/ 1967 Chester 230-101 2,676,575 4/ 1954 Rosenberger 103-272 X ROBERT M. WALKER, Primary Examiner.

W. I. KRAUSS, Assistant Examiner. 

